Field of the Invention
The present invention relates generally to methods and devices for analyzing and mapping soil properties within a field. In particular, the present invention relates to methods and devices for collecting and mapping soil reflectance data on-the-go.
Description of the Related Art
Variations in soil properties can be detected, even with the human eye, based on differences in light reflectance. Darker soils contain higher levels of moisture or organic matter than light-colored soils. Molecules containing C—H, O—H, or N—H bonds that are exposed to light vibrate due to the force of the electric field. This vibration absorbs optical energy so that less light is reflected off the soil. While this can be detected visually, light sensors, especially those in the near infrared (NIR), can quantify the reflectance characteristics and provide the data needed to develop calibrations to soil properties. Soil reflectance has been studied extensively since the 1970s and is widely reported in the scientific literature as an effective means for approximating soil organic matter and carbon. There have been some uses of bare soil photographs where the darker areas were correlated with higher organic matter levels, but with the increased use of conservation tillage and no-till farming, the ability to collect such images has diminished. Rudimentary devices to collect reflectance data in the field, operating near or under the soil surface, were mobilized in the early 1990s. Due to several limitations in their designs, neither of these was fully commercialized.
Since the advent of GPS-enabled precision farming in the mid-1990s, growers have sought ways to better delineate areas of contrasting productivity within their fields. Yield maps produced by combine yield monitors and remote crop imagery both show annual crop differences, but relating those temporal variations to fundamental productivity zones has proven challenging due to the many factors affecting crop growth. Soil surveys produced by the USDA have also been examined, but the scale at which these were created is too coarse to show many important inclusions of varying soils. On-the-go sensors to measure other soil properties have been developed and widely commercialized, including one that measures soil pH, and several that relate soil electrical conductivity measurements to soil texture and soil salinity. These proximal sensors collect dense datasets and their widespread use has generated an awareness of soil spatially variability within fields. None of these commercial sensors measures soil organic matter consistently.
Organic matter is an important factor in crop growth, as it affects soil moisture infiltration and retention, soil tilth, rooting depth, soil-applied herbicide activity, nitrogen release, and other aspects of nutrient cycling. A precise map of organic matter will provide growers with an important piece of information as they seek to vary nitrogen, seed population, herbicides, and other inputs.
Veris Technologies Inc., the assignee of the present application, began development of soil optical devices in 2002 and has described a commercialized spectrophotometer system for mapping soil in its U.S. Patent Publication No. 2009-0112475 (Christy et al.). That system includes a field-deployed implement containing costly visible and near-infrared spectrometers, which collect spectra that include over 300 individual wavelengths. That level of technology is needed in soil research and where carbon measurements require an extremely high level of precision, but is not practical for grower and consultant use due to expense and complexity.
There is a need in the industry for a mapping system suitable for grower and consultant use, which is capable of providing accurate, useful soil organic matter measurements using a simple, low cost design.